Field of the Invention
The invention relates to a device for automatically changing printing plates in a printing machine.
When printing plates are being changed, on the one hand, it is imperative that a new printing plate be fed to the plate cylinder in register. On the other hand, it is likewise necessary to ensure that the printing plate be fed in without scratching.
For the purpose of register-maintaining alignment of the infed printing plate, the plate cylinder usually has register pins, which engage in assigned cut-outs formed on the leading edge of the printing plate. During this procedure, a given (slight) lateral compensating movement of the printing plate may occur. In order to avoid the risk entailed thereby of scratching the printing plate surface, the conveying drive must be conceived so that relative movements between the laterally moving printing plate and the transport rollers cooperating with the printing plate are avoided, if possible.
A device of the general type designated at the introduction hereto has become known heretofore from the published German Patent Document DE 44 04 558 C2. In the subject matter of this document, the lateral compensating movement of the printing plate without friction and therefore without scratches is made possible by the fact that driven transport rollers and corresponding counter-pressure or reaction rollers are mounted so as to be movable in the axial direction of the plate cylinder. This heretofore known construction necessitates a quite considerable expenditure for design and, therefore, is costly.
It is accordingly an object of the invention of the instant application to provide a device for automatically changing printing plates in a printing machine wherein an expenditure for achieving a scratch-free lateral compensating mobility of the printing plate is reduced.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a device for automatically changing printing plates in a printing machine having a plate cylinder to which the printing plate is to be fed and on which the printing plate is to be fixed detachably, comprising a transport system for conveying the printing plate while permitting axial compensating movements thereof, the transport system having at least one driven transport roller and an air cushion for holding the conveyed printing plate in contact with the transport roller, the plate-holding air cushion being formed between the counterpressure element, on one side, and the printing plate, on the other side.
In accordance with another feature of the invention, compressed-air nozzles are formed as at least one of the counterpressure element and at least one constituent part of the counterpressure element, respectively, the nozzles being arranged spaced apart from one another, at least in a conveying direction of the printing plate, and being directed at least approximately perpendicularly to the printing plate guidable between the counterpressure element and the transport roller.
In accordance with a further feature of the invention, the compressed-air nozzles are of slit-like construction and have a slit length corresponding approximately to the width of the printing plate being conveyed.
In accordance with an added feature of the invention, the compressed-air nozzles are round nozzles, and are disposed spaced apart from one another both in the conveying direction of the printing plate and in a direction transverse thereto. In accordance with an additional feature of the invention, the printing plate is insertable in at least approximately vertical direction into the transport system, and wherein the air cushion serves for deflecting the printing plate, during transport thereof, in a direction towards the plate cylinder by utilizing flexibility of the printing plate in the process.
In accordance with yet another feature of the invention, the counterpressure element has a housing with a compressed-air supply, the compressed-air nozzles being arranged on a face of the housing of the counterpressure element facing towards the printing plate being conveyed.
In accordance with yet a further feature of the invention, the face of the housing of the counterpressure element facing towards the printing plate being conveyed has compressed-air nozzles formed therein and has a curvature at least approximately corresponding to the curvature of the printing plate being conveyed.
In accordance with yet an added feature of the invention, the housing of the counterpressure element, on a rear side of the housing, facing away from the printing plate being conveyed, is formed with a face at least approximately matching the face of said housing facing towards the printing plate being conveyed.
In accordance with a concomitant feature of the invention, the compressed-air nozzles are formed as throttle slits and bore holes, respectively.
An advantage of the invention when compared with the prior art outlined hereinabove is that only the driven transport roller or rollers have to be mounted laterally, i.e., in the axial direction of the plate cylinder, but not the air cushion which holds the printing plate in contact with the transport roller or rollers for automatically changing printing plates in a printing machine. This is because the air cushion according to the invention permits the printing plate to be pressed against the drive roller or rollers without contact and, therefore, without friction.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device for automatically changing printing plates in a printing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.